In recent years, with regard to an AC motor to be mounted in a vehicle such as an automobile, the demand for reduced noise and reduced vibration has been being raised in order to improve the silence in the vehicle and the steering feeling of a driver.
Patent Document 1 discloses a technology in which with regard to armature windings of a brushless motor, two different three-phase windings are wound in such a way as to be multiplexed with a slot pitch of the electric angle [(360×P)/(s×2)]—letting P and s denote the number of poles and the number of slots, respectively—, the armature windings are energized with a phase difference angle corresponding to the slot pitch, and the gap between the stator and the rotor is set to become a magnetic skew, in a sense of an electric angle, that is twice as large as the phase difference angle between the foregoing slots, so that the torque ripples, which are the 6th- and 12th-components of the electric angle and are produced in the brushless motor are reduced and hence the vibration and noise of the motor are decreased.